This invention relates to a pressure relief valve for pneumatic powered guns, and, more particularly, to a pressure relief valve which prevents excessive loss of pressure when air is vented to limit the maximum muzzle velocity.
A pneumatic or air powered gun conventionally includes a pressure reservoir for storing pressurized air and firing means for releasing the pressurized air to propel a projectile out of the barrel. Pressure is usually built up in the reservoir by a hand pump mounted on the gun, and the pressure in the reservoir is increased each time the pump is operated. However, variations in the amount of pumping affect the performance of the gun. Excessive muzzle velocity caused by over-pumping violates government regulations in some jurisdictions. Excessive pressure also causes abnormal wear and damage to components of the gun. Over-pumping can also result in all of the pressure not being released when the gun is fired, and an unexpected discharge might occur without the gun being pumped if the trigger is again pulled. Under-pumping creates a weak muzzle velocity and inaccurate shots.
Pressure relief valves have been employed to control the maximum pressure in guns and other devices. For example, U.S. Pat. Nos. 1,486,215, 3,025,633, and 3,680,540 disclose valves for shunting air away from the projectile to reduce muzzle velocity when the pressure reaches a certain limit. However, performance can be affected by surging and the resulting excessive loss of pressure. For example, assume that it is desired to limit the pressure to that which provides a muzzle velocity of 500 feet per second (fps). The last pump which increases the pressure over the desired maximum will open the pressure relief valve, and sufficient pressure might escape before the valve closes to reduce the muzzle velocity substantially below 500 fps. The resulting low pressure not only causes low muzzle velocity but can also cause jamming.
The invention controls maximum muzzle velocity of the gun while minimizing surging and loss of excessive amounts of pressure. A check valve includes a spring-biased plunger which fits relatively snuggly in the housing of the check valve and which normally closes the air inlet of the check valve. The valve housing has a relatively small air outlet orifice which creates backpressure when the plunger moves away from the air inlet. The backpressure and the snug fit between the plunger and the valve housing restrain movement of the plunger and permit the spring to return the plunger to its sealing position almost immediately after the pressure in the gun falls below the desired maximum.